Devices which are used to indicate the slope of a surface are generally known as levels and are used by various skilled tradesman, particularly those skilled in the construction field. For example, a rough carpenter often needs to know if a wall is perfectly vertical or "plumb." A mason, after laying a course of bricks, needs to know if the newly laid course is horizontal. A plumber often needs to install drainage pipe with a certain prescribed slope so that the contents of the pipe will drain properly. These are all applications in which a skilled tradesman would typically employ the use of a level.
Numerous types of level devices have been available for years. These devices have typically employed as their slope sensor, a hermetically sealed, clear glass tube filled partially with a liquid and partially with a gas. The tube is constructed with a slight arc in its midsection so that when it is properly oriented, the gas contained inside of it will rise to the highest portion of the arched section. This tube is fixed to a member having at least one substantially straight edge, and the face if the tube is indexed so that the gas bubble is centered in the indices when the straight edge of the member lies in a substantially horizontal or vertical plane.
Although the above-mentioned level, typically known as a bubble level or spirit level, has been used for may years, it is not without its drawbacks. For example, it cannot be used in situations where the ambient light is insufficient to allow the operator to view the liquid-filled tube. Another disadvantage of the bubble level is that it typically cannot be used to accurately measure inclines which are not perfectly horizontal or vertical. A number of improvements to the traditional bubble level have been introduced recently in an attempt to overcome its inherent problems. Most of these improvements concentrate in the area of improving the sensor used to sense incline and the use of electronics to condition and present slope information.
One such device which uses electronics to aid in the measurement of sloped surfaces is disclosed in U.S. Pat. No. 4,592,147 issued to Herman on June 3, 1986. This patent uses a pendulum immersed in an oscillation damping liquid as the fundamental sensor for measuring slope. The pendulum is suspended within a light path, thereby causing an electrical output indicating when the pendulum is in a predetermined position. This predetermined condition can be calibrated to represent a vertical, horizontal or any predetermined position. This patent abandons the use of a bubble-filled tube as the fundamental sensor of slope. The device disclosed in Herman suffers from one of the same drawbacks as that of the traditional bubble level inasmuch as it cannot measure graduations of slope such as 1 degree, 2 degrees, etc. Further, the pendulum sensor only has the capability of sensing a single orientation. For example, if the device disclosed in Herman is to be used to measure both a 0 degree slope and a 90 degree slope, two separate sensors would have to be incorporated in the indicating device; one sensor would be used for vertical measurement, and the other would be used for horizontal measurement.
Another level detecting device which employs a device similar to a pendulum as the fundamental sensor of slope is disclosed in U.S. Pat. No. 4,668,846 issued to Klumpp on May 26, 1987. This device is similar to that disclosed in Herman in that it does not use a bubble level for sensing slope. Klumpp teaches a gravity-sensing rotor which has various electrical contacts disposed on the rotor. When the rotor is oriented in certain preselected positions, the electrical contacts provide a current path, thereby switching current to various information output terminals. Klumpp does not teach the use of a chamber, partially filled with liquid, as the fundamental means for detecting surface slope. The device disclosed in Klumpp must be externally illuminated whenever the ambient light conditions are insufficient for viewing.
U.S. Pat. No. 4,563,822 issued to Legris on Jan. 14, 1986 discloses a level device for masonry work which uses a combination of a flexible tube filled with a liquid, a plurality of chambers and diaphragms and needle-type contacts which indicate a point which may be higher or lower than a predetermined level. This device cannot be used to measure vertical slopes in that it is only sensitive to differences in height.
Other level detecting devices of the type which use electronics are disclosed in the May 1989 issue of Popular Science. One such level marketed by Wedge Innovations termed the SmartLevel.TM. uses an advanced digital electronic circuit consisting of a patented microcalculator and gravity-leveling sensor housed in a tough, polycarbonate module. Further details on the gravity-leveling sensor are not disclosed in the Popular Science article. Another level disclosed in the May 1989 issue of Popular Science is one marketed by Zircon International and is called the Anglesensor.TM.. The Anglesensor is built around an optically-sensed pendulum. The pendulum swings in one plane and bisects a path of infrared light. The Anglesensor does not use a cylinder partially filled with a liquid for sensing slope.
Accordingly, it is a primary object of the present invention to provide an electronic level for sensing the incline of a surface.
A further object of this invention is to provide an electronic level which indicates the incline of a surface in calibrated graduations.
Still another object of this invention is to provide a device which indicates the amount of incline of a surface by monitoring the electrical resistivity of an electrically conductive fluid.
Still another object of this invention is to provide an electronic level which is self-illuminating and provides for an automatic brightness control as a function of ambient light conditions.
Still a further object of the present invention is to provide an electronic level which detects horizontal and vertical slopes.
Yet another object of the invention is to provide an electronic level having a standby mode for conserving battery power.
Yet another object of the invention is to provide a digital level having an error display circuit for indicating when the level is oriented in a position which is inconsistent with its ability to detect the slope of a surface.